Apparatus and method for recovery of dry oil gas tar



Oct. 4, 1955 E. s. PETTYJOHN APPARATUS AND METHOD FOR RECOVERY OF DRY OIL GAS TAR Filed Feb. 15, 1952 United States Patent Elmore S. Pettyjohn, Evanston, Ill., assignor to The Institute of Gas Technology, Chicago, 111., a corporation of Illinois Application February 13, 1952, Serial No. 271,315 7 Claims. (Cl. 196-76) This invention relates to a plant for making high heating value oil gas and to a method for making high heating value oil gas without at the same time producing aqueous tar emulsions as by-products.

it is conventional to produce a high heating value oil gas (about 900 to 1200 B. t. u./s. c. f.) by cracking petroleum oils in a steam atmosphere. The products then obtained include a high heating value oil gas, carbon and tars. The carbon is deposited in the vessel wherein cracking is eifected and may be removed from time to time by interrupting the cracking and burning off the carbon. Before such carbon is burned off, the cracking vessel is purged with steam. The tars are formed as vapor admixed with the oil gas. Thus, the hot gaseous mixture issuing from the cracking vessel is made up of tar vapor, oil gas and steam. This gaseous mixture is separated into its three components by conventional methods including passing the gaseous mixture sequentially through a wash box containing water forming a liquid seal and also serving to cool the hot gaseousmixture, through a relief holder, through a primary cooler, through an exhauster, through a tar extractor, through a final cooler and into a station holder. Tar in liquid form is deposited in all these structures, from the wash box on downstream. Particularly large amounts of tar are deposited in the primary cooler. The steam is also condensed as water, mainly upstream of the tar extractor. Thus, the steam and the bulk of the tar are condensed simultaneously, mainly in the wash box and in the primary cooler. As a result, emulsions of tar in water are formed, particularly in the wash box and in the primary cooler. In the latter structure, there are formed two separate layers: an upper water layer and a lower layer of aqueous tar emulsion. Although it is easy to separate these two layers, it isdiificult to separate from each other the two immiscible liquids present in the tar emulsion.

It is therefore an important object of the present invention to provide method and apparatus for making oil gas capable of eliminating the formation of tar-in-water emulsions encountered in conventional methods of making high heating value oil gas and yielding (instead of tar emulsions) a dry tar as a final by-product.

Other and further objects and features of the present invention will become apparent from the following description and appended claims as illustrated by the accompanying drawing showing, diagrammatically and by way of an example, an apparatus according to the present invention in vertical longitudinal cross section, parts being shown in elevation.

According to the present invention, dry tar, and not water, is employed in the wash box as a sealing liquid. The tar obviously will prevent the entry of gases into the cracking vessel through the make gas outlet duct equally as well as the water conventionally employed as a sealing liquid. But the dry tar in the wash box is by itself incapable of performing the gas COOIiDgIfunCiiOD performed by the water conventionally"employed as a cooling medium. To effect the cooling of the make gas, I introduce water into the wash box (or into the gas duct upstream of the wash box) in an amount suflicient to effect the necessary cooling by complete evaporation of the water. Further, the amount of water introduced into the wash box is limited to maintain the temperature of the tar in the wash box above2l2 F., say at 250 to 300 F, the tar in the wash box remaining substantially dry in spite of the addition of water (which is completely evaporated). The steam thus generated is admixed with the gaseous mixture flowing through the wash box and is condensed downstream of the wash box, principally in the primary cooler and there, along with any steam present in the gaseous mixture issuing from the cracking vessel, forms the above noted two layer condensate. The tar emulsion forming one of these two layers (after separation from the water forming the other layer) may be and preferably is introduced into the wash box to supply the water for cooling the gas passing through the wash box by complete evaporation of the total water content of the emulsion. In other words, the initial cooling of the hot make gas issuing from the cracking vessel can be effected by recirculating a body of water between the wash box and the primary'cooler. The tar condensed in the primary cooler in the form of an emulsion is then also transferred to the wash box, so that dry tar will continuously overflow from the wash box.

When operating according to my invention disclosed in the next preceding paragraph, no tar emulsions are formed in the wash box. If any tar emulsions are formed in the'primary cooler (or elsewhere), these emulsions have their water contents removed when transferred to the wash box where the water contents are evaporated off when cooling the hot gaseous mixture issuing from the cracking vessel. In brief, all the tar is obtained ultimately in dry form, rather than as an emulsion in water, and the bulk of this dry tar can be collected at a single place. The tar collected downstream of the primary cooler (which even in the case of conventional processes ordinarily is dry) forms only a small portion of the total amount of tar produced.

Referring now to the drawing, there is shown a gas generating apparatus including a generator 10 and a superheater 12 connected at their bottoms by a duct 14. Thegenerator 10 and superheater 12 are both provided with layers of closely spaced oil cracking checker bricks 16 arranged in closely overlapping position (as between the various layers) so as to provide a maximum number of tortuous gas passages whereby highly eflicient heat exchange between the gas and the brick work is promoted. Due to the overlapping of the checker bricks, the brick structure forms a unified mass perforated by a large number of gas passages, with the result that the temperature therein will be substantially uniform. The cracking of the oil and of the oil gas will, therefore, be uniform throughout the brick wor The roof of the generator 10 is arched above the brick work and formed with a central vertical aperture 18 through which discharges an air duct 20 provided with a valve 22. An oil pipe 24 having a valve 26 and terminating in a spray device extends through the air duct 20 and the aperture 18 into the generator 10 as does also a steam pipe 28 having a valve 30.

The roof of the superheater 12 is arched above the brick work and is formed with a central vertical vent aperture 32 closed by a valve 34. A stack 36 is arranged above the valve 34 for removing gases discharged through the vent aperture 32. The arched roof of the superheater 12 is also formed with an aperture 38 receiving one end of a make gas exit duct 40 bent over elbow-wise to provide a dependent terminal portion dipping into 'dry tar serving as a sealing liquid 42 in an enclosed wash box 44. A main gas duct 46 opens into the wash box 44 above the liquid level therein. The wash box 44 may be provided with a seal pct 48 and a drain pipe 50. The main gas duct 46 discharges into a vertical condenser generally indicated at 52 and provided with a water jacket 54 having an inlet 56 for cold water and an outlet 58 for water that has passed through the jacket 54. in the drawing, the duct 46 is not shown as a single communicating duct between the wash box 44 and the condenser 52, but for the sake of clarity is broken ofi a short distance from each of its terminals. It is to be understood that one continuous duct is provided. The uncondensed oil gas passes through a conduit 60 to an exhauster (not shown), while the liquid condensate (including tar and water) flows through a conduit 62 to a closed vessel 64 (located above the gas duct 40 and above the wash box 44) Where the condensate stratifies to form a lower Water layer 66 and an upper tar emulsion layer 63. The water layer 66 may be drained off from time to time through a valved pipe 70 piercing the bottom of the vessel 64 and projecting thereabove, if at all, only for a short distance. The tar emulsion 68 may be drained from the vessel 64 by either or both of two valved conduits 72 and 74 which both pierce the bottom of the vessel 64 and project thereabove for a substantial distance so as to reach the layer of tar emulsion 68. The conduit 72 extends into the last (vertical) portion of the gas conduit 46 and may have a terminal spray device 76 for spraying tar emulsion into the hot gas passing through the duct 40 shortly before this gas enters the wash box 44. The conduit 74 pierces the roof of the wash box 44 and projects into the tar layer 42 therein. The depth of the tar layer 42 in the wash box 44 is determined by overflow into a pipe 78 which drains into the seal pot 48 from which the tar flows through a pipe 80 into the drain pipe 50.

In the operation of the apparatus of the drawing, the generator and superheater 12 are initially heated to cracking temperatures (l350 to l800 5., depending upon the oil to be cracked and the rate of oil feeding into the generator). For this purpose, the valve 34 is raised to open the vent 32, the valve 22 is opened to admit air through the duct 24) into the generator 10, the valve 26 in the oil pipe 24 is opened to spray oil into the generator, and the valve 36 in the steam pipe 28 is opened. The oil is burned in the generator 16 and the combustion gases flow downwardly through the generator 16, through the duct 14, upwardly through the superheater 12 and out through the vent aperture 32 into the stack 36. if any carbon is present in the generator 10 and superhenter 12 (as by way of deposit formed in a preceding make step), this carbon is then burned off. Such a heating and carbon removing step or stage is carried out in the manner conventional in connection with the operation of cyclic oil cracking apparatus of conventional construction.

After cracking temperatures have been reached in the generator 19 and superheater 12, the valve 22 in the air duct 23 is closed. The valve 26 in the oil pipe 24 may then be closed for a short period of time so that the steam issuing from the pipe 36 may purge the generator 10, the duct 14 and the superheater 12. Next, the valve 34 is closed and the valve 26 in the oil pipe 24 is again opened. Then the oil sprayed into the generator 10 is cracked in the brick work therein, and the oil gas thus produced flows through the duct 14 into and through t e superheater 12 where further cracking of the oil and gas takes place.

When the generator 10 and superheater 12 have cooled ofl in the course of the make period to a temperature at the lower end of the cracking temperature range, the valve 26 in the oil pipe 24 is closed and the oil gas remaining in the apparatus is purged by the steam flowing from the conduit 28. After such purge, another blast is carried out, to raise the temperature of the brick work 16 and to remove therefrom carbon deposited during the make period.

When the apparatus of the drawing is operated as described, the make gas formed in the make periods flows through the duct 40, through the tar 42 in the wash box 44 (where it is cooled, as described hereinbelow), through the duct 46, through the condenser 52 and through the duct 60. Some tar, but no water, is condensed in the wash box 44, for the tar layer 42 is maintained above 212 F. But large amounts of water and of tar are condensed from the gas in the condenser 52 and flow through the duct 62 into the vessel 64 to form the water layer 66 and the tar emulsion layer 68. The water may be drained from time to time through the pipe 70. The tar emulsion may be sprayed through the pipe 72 into the gas passing through the duct 40 or, if desired, may be allowed to flow through the pipe 74 into the tar layer 42 in the wash box 44. In either event, the rate of flow of tar emulsion is adjusted so as to keep the tar 42 above 212 F., in other words, so that the total water content of the tar emulsion is evaporated by the heat content of the gas issuing from the superheater 12 through the duct 40. However, the tar emulsion is caused to flow at a rate sufiicient to maintain the tar layer 42 relatively cool, say, at a temperature of from 250 to 300 F.

As a result of the continuous flow of tar emulsion into the wash box 44, dry tar overflows continuously from the wash box 44 through the pipe 78 into the seal pot 48. From this pot 48, the tar overflows through the pipe 80 into the pipe 50 which may discharge into any suitable receptacle. Note that the pipe 78 dips into the tar in the pct 48, while the pipe 80 projects for a substantial distance into the pot 48, so that the tar in the pot 48 functions as a seal to maintain any pressure existing within the wash box 44. V

The operation of the apparatus as so far described relates to an improvement in a conventional method of cracking the petroleum oils in which the cracking is carried out in an atmosphere of steam. Reference is made to two copending applications of myself and Henry R. Linden. One of these applications is entitled Method of Making Oil Gas Interchangeable With Natural Gas, Serial No. 270,957, filed February 11, 1952. Another applicationis entitled Oil Gas Plant, Serial No. 270,956, filed February 11, 1952, now abandoned. These applications show novel methods of cracking petroleum oil in atmospheres of oil gas or natural gas or methane. Steam is injected into the cracking apparatus only for purging purposes. These methods can be practised in apparatus described in said copending applications which include at least one generator-superheater set (which can be identical in construction with the set shown in the drawing of the present application), a make gas discharge duct, and a wash box. The novel methods of the said copending applications can be further improved to produce dry tar as a by-product by modifying the methods of the copending applications as taught in the present application. Thus, instead of injecting steam through the pipe 28 to provide a steam atmosphere in the cracking or make stage, this pipe may be utilized to inject oil gas or natural gas. Thus, oil gas or natural gas is substituted for the steam conventionally injected during the make period in conventional cracking methods, with the result that only a very limited amount of steam (injected for purging purposes) is condensed along with tar in the primary condenser in the apparatus of the present application. In that event, only tar emulsions may be formed in the vessel 64, and it may even be necessary to add water in an amount suflicient to provide the above indicated cooling by evaporation of water in the wash box 44.

Many details of construction and procedure may be varied without departing from the principles of this invention, and it is therefore not my purpose to limit the patent granted on this invention otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. Apparatus for cracking a petroleum oil with formation of oil gas and of tar, said apparatus being adapted for recovery of said tar in dry form and comprising a vessel for cracking said petroleum oil, a duct for discharging from said vessel the product of said cracking in the form of a hot gaseous mixture, an enclosed wash box arranged to receive said hot gaseous mixture and containing a layer of dry tar, said duct having a discharge end dipping into said layer of tar, a pipe having its discharge end communicating with said wash box for adding cooling liquid, including water, to said tar whereby evaporation of said water may maintain said tar at a temperature above 212 F. but below the temperature of said hot gaseous mixture, drain means for tar accumulated in said wash box, a conduit for discharging from said wash box a steamcontaining mixture of oil gas and tar vapor, a condenser for liquefying said steam and said tar vapor in said mixture discharged from said wash box, and a receptacle for the resulting condensate, drain means for removing water from said receptacle, the opposite end of said pipe communicating with said receptacle whereby any tar emulsion formed as a result of said condensation may be conducted into said pipe for flow therethrough to said wash box as the cooling liquid for the layer of tar therein.

2. Apparatus according to claim 1 in which said pipe discharges into said duct.

3. Apparatus according to claim 1 in which the means for draining accumulated tar from the wash box comprises an overflow pipe for said wash box and a receptacle for dry tar overflowing from said wash box through said overflow pipe.

4. A method for cracking petroleum oil with the formation of oil gas and tar, said method being adapted for recovery of said tar in dry form and comprising cracking said oil at an elevated temperature to form a hot mixture of oil gas and tar vapor, bubbling said hot mixture through liquid tar to condense substantially all the tar vapors in said mixture as dry tar, adding water to said liquid tar to maintain the temperature thereof below the temperature of the hot gaseous mixture, but above 212, and condensing the steam and normally liquid vapors from the gaseous mixture that has been bubbled through the tar.

5. A method for cracking petroleum oil with the formation of oil gas and tar, said method being adapted for recovery of said tar in dry form and comprising cracking said oil at an elevated temperature to form a hot mixture of oil gas and tar vapor, intimately contacting said hot mixture with liquid tar to condense substantially all the.

tar vapors in said mixture as dry tar, adding cooling liquid to said liquid tar to maintain the temperature thereof below the temperature of the hot gaseous mixture, but above 212', and condensing the normally liquid vapors, including cooling liquid and any remaining non-condensed tar vapors, from the gaseous mixture that has been contacted with the tar, said cooling liquid added to the liquid tar comprising the product of said last condensing step and including water.

6. The method of claim 5 in which the cooling liquid is sprayed into said hot gaseous mixture before said hot gaseous mixture is bubbled through the tar.

7. The method of claim 5 in which a portion of the cooling liquid is sprayed into said hot gaseous mixture before said hot mixture is bubbled through the tar, and the remainder is added directly to the liquid tar.

References Cited in the file of this patent UNITED STATES PATENTS 654,258 Ihart July 24, 1900 1,589,374 Dietzsch June 22, 1926 1,958,583 Miller May 15, 1934 2,067,450 Imes Jan. 12,1937 

1. APPARATUS FOR CRACKING A PETROLEUM OIL WITH FORMATION OF OIL GAS AND OF TAR, SAID APPARATUS BEING ADAPTED FOR RECOVERY OF SAID TAR IN DRY FORM AND COMPRISING A VESSEL FOR CRACKING SAID PETROLEUM OIL, A DUCT FOR DISCHARGING FROM SAID VESSEL THE PRODUCT OF SAID CRACKING IN THE FORM OF A HOT GASEOUS MIXTURE, AN ENCLOSED WASH BOX ARRANGED TO RECEIVE SAID HOT GASEOUS MIXTURE AND CONTAINING A LAYER OF DRY TAR, SAID DUCT HAVING A DISCHARGE END DIPPING INTO SAID LAYER OF TAR, A PIPE HAVING ITS DISCHARGE END COMMUNICATING WITH SAID WASH BOX FOR ADDING COOLING LIQUID, INCLUDING WATER, TO SAID TAR WHEREBY EVAPORATION OF SAID WATER MAY MAINTAIN SAID TAR AT A TEMPERATURE ABOVE 212* F. BUT BELOW THE TEMPERATURE OF SAID HOT GASEOUS MIXTURE, DRAIN MEANS FOR TAR ACCUMULATED IN SAID WASH BOX, A CONDUIT FOR DISCHARGING FROM SAID WASH BOX A STEAMCONTAINING MIXTURE OF OIL GAS AND TAR VAPOR, A CONDENSER FOR LIQUEFYING SAID STEAM AND SAID TAR VAPOR IN SAID 